CVE-2026-98067 erofs: disable LZ4 rolling decompression for now
A flaw in Linux kernel EROFS LZ4 rolling decompression causes memory corruption due to unsafe backward copying, potentially leading to data leaks or system crashes.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-98067?
CVE-2026-98067 is a memory corruption vulnerability in Linux, published on 25 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
erofs: disable LZ4 rolling decompression for now
LZ4 rolling decompression [1] was introduced to reduce the memory footprint of temporary pages:
For many cases, it is needed for users to read small data within a compressed extent (pcluster), either due to random small read, or since uptodate folios (typically order-0) cannot be reused for decompression again since decompression algorithm refills already-uptodate folios.
Rolling decompression works because LZ4 is LZ77-based and only refers to the most recent 64 KiB of decompressed data, so in theory only a bounded rolling window of temporary pages is needed when decompressing.
It can save a lot of temporary memory, e.g. 601,960-byte data can be compressed into a 256k LZ4 compressed extent, which means it needs 146 extra pages per request in the worst case if rolling decompression is disabled.
However, the upstream LZ4 implementation is not under EROFS' control: For example, the literal copy memmove() may still **copy long literals backward** on x86 based on the address comparison even when the source and destination ranges do not overlap (IOWs, inline decompression doesn't need to be considered here). That breaks the rolling assumption and makes the optimization broken.
Disable it for now to make sure the data correctness first since EROFS is used everywhere now: The rolling window approach can be revived once we either ensure that the official LZ4 code always copies forward for non-overlapping ranges or maintain our own LZ4 implementation in EROFS.
The main impact is a higher runtime memory footprint; However, recent commit 0f6273ab4637 ("erofs: add a reserved buffer pool for lz4 decompression") helps mitigate this when enabled but it's still not perfect.
[1] https://www.usenix.org/conference/atc19/presentation/gao § 3.3 Decompression
Which versions are affected by CVE-2026-98067?
How do I fix CVE-2026-98067?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-98067 being exploited?
There is no known exploitation of CVE-2026-98067 in the wild and no public exploit code.
Sources
Also known as AZL-104828, BELL-CVE-2026-98067, DEBIAN-CVE-2026-98067, GHSA-37cq-5ff4-fh64, UBUNTU-CVE-2026-98067.